Optical packet exchanger

ABSTRACT

An optical packet exchanger is provided which, in a situation where a transmission path for an optical packet is to be switched by using an address signal, prevents the transmittable capacity for the information signal from being decreased, and which facilitates the extraction of the address signal even if the modulation speed for the information signal becomes high. An optical modulation section  102  outputs an optical packet obtained by subjecting output light from a light source  101  to an intensity modulation using an information signal and a phase modulation using an address signal corresponding to a transmission destination for the information, signal. An optical splitter section  301  splits the optical packet received via the optical transmission section  200  into two optical packets. An address reading section  302  reads the address signal from the phase of one of the optical packets output from the optical splitter section  301.  Based on the address signal output from the address reading section  302,  a path switching section  303  determines an output port for the other optical packet

TECHNICAL FIELD

The present invention relates to an optical packet exchanger, and moreparticularly to an optical packet exchanger for switching a transmissionpath for an optical packet signal by using an address signal.

BACKGROUND ART

An example of a conventional optical packet exchanger for switching atransmission path for an optical packet signal by using an addresssignal is a device disclosed in, for example, K. SETO et al., “giga-bitEthernet textbook”, multimedia tsushin kenkyukai, ASCII corporation,March 1999. FIG. 11 is a block diagram illustrating an exemplarystructure of this conventional optical packet exchanger.

In FIG. 11, the conventional optical packet exchanger is composed of anoptical transmitter section 1000, an optical transmission section 2000,and a router section 3000. The optical transmitter section 1000comprises a light source 1001, an optical modulation section 1002, and adata generation section 1003. The router section 3000 comprises anoptical splitter section 3001, a photoelectric conversion section 3004,an address extraction section 3005, and a path switching section 3003.The light source 1001 outputs continuous light. The data generationsection 1003 generates a data signal, which includes an informationsignal to be transmitted plus a header, the header being an addresssignal corresponding to a transmission destination of the informationsignal. The optical modulation section 1002 subjects the continuouslight which is output from the light source 1001 to an intensitymodulation, using the data signal generated by the data generationsection 1003. The optical splitter section 3001 splits an opticalpacket, which is input via the optical transmission section 2000, intotwo. The photoelectric conversion section 3004 converts one of theoutput optical packets from the optical splitter section 3001 into anelectrical signal. As a result of this process, the data signal is takenout of the optical packet. The address extraction section 3005 removesthe information signal from the data signal which has been taken out bythe photoelectric conversion section 3004. As a result of this process,the address signal is extracted. In accordance with the address signalwhich has been extracted by the address extraction section 3005, thepath switching section 3003 determines the path for the other outputoptical packet from the optical splitter section 3001.

However, the aforementioned conventional optical packet exchanger has aproblem in that, since a data signal to which the address signalcorresponding to the information signal is added as a header is used,the transmittable capacity is decreased by the amount corresponding tothe address signal; that is, the transmission efficiency is decreased.In addition, when the modulation speed for the information signalbecomes high, the modulation speed for the address signal also becomeshigh. This makes it difficult for the address extraction section 3005 inthe router section 3000 to read the address signal.

Therefore, an object of the present invention is to provide an opticalpacket exchanger which, in a situation where a transmission path for anoptical packet is to be switched by using an address signal, preventsthe transmittable capacity for the information signal from beingdecreased due to the increased transmission size ascribable to theaddress signal, and which facilitates the extraction of the addresssignal even if the modulation speed for the information signal becomeshigh.

DISCLOSURE OF THE INVENTION

The present invention is directed to an optical packet exchanger forswitching a transmission path for an optical packet which constitutes aburst-type optical signal. In order to achieve the above object, theoptical packet exchanger according to the present invention comprises anoptical transmitter section, an optical transmission section, and arouter section.

The optical transmitter section transmits an optical packet, on which aninformation signal and an address signal corresponding to a transmissiondestination for the information signal are superposed by differentmodulation methods. The optical transmission section propagates anoptical packet transmitted from the optical transmitter section. Therouter section receives the optical packet via the optical transmissionsection, and switching a transmission path for the optical packet basedon the address signal which is extracted from the optical packet.Preferably, a modulation speed for the address signal and a modulationspeed for the information signal are different.

The optical transmitter section may have either one of the followingstructures, for example. The optical transmitter section may include alight source for outputting continuous light, and an optical modulationsection for outputting an optical packet which is obtained by subjectingthe output light from the light source to an intensity modulation usingthe information signal and a phase modulation using the address signal.Alternatively, the optical transmitter section may include a lightsignal source for outputting continuous light having been subjected toan intensity modulation using the information signal, and an opticalmodulation section for outputting an optical packet which is obtained bysubjecting the output light from the light signal source to a phasemodulation using the address signal. Alternatively, the opticaltransmitter section may include a light signal source for outputtingcontinuous light having been subjected to a phase modulation using theaddress signal, and an optical modulation section for outputting anoptical packet which is obtained by subjecting the output light from thelight signal source to an intensity modulation using the informationsignal.

The router section may have either one of the following structures, forexample. The router section may include: an optical splitter section forsplitting the optical packet received via the optical transmissionsection into two optical packets; an address reading section for readingthe address signal based on phase information of one of the opticalpackets output from the optical splitter section; and a path switchingsection having a plurality of output ports and selecting, based on theaddress signal read by the address reading section, one of the pluralityof output ports from which to output the other optical packet outputfrom the optical splitter section. Alternatively, the router section mayinclude: an optical splitter section for splitting the optical packetreceived via the optical transmission section into two optical packets;an address reading section for reading the address signal based on phaseinformation of one of the optical packets output from the opticalsplitter section; an optical phase adjustment section for adjusting aphase of the other optical packet output from the optical splittersection to a constant phase value, based on the address signal read bythe address reading section; and a path switching section having aplurality of output ports and selecting, based on the address signalread by the address reading section, one of the plurality of outputports from which to output the other optical packet whose phase has beenadjusted to the constant phase value by the optical phase adjustmentsection.

A typical optical modulation section comprises: an optical splittersection for splitting the output light from the light source into twolight portions; a first splitter section for splitting the addresssignal into two address signals; a second splitter section for splittingthe information signal into two information signals; a phase inversionsection for inverting a phase of one of the information signals outputfrom the second splitter section; a first synthesis section forcombining one of the address signals output from the first splittersection with the information signal whose phase has been inverted by thephase inversion section, to output a first synthesized signal; a secondsynthesis section for combining the other address signal output from thefirst splitter section with the other information signal output from thesecond splitter section, to output a second synthesized signal; a firstwaveguide for subjecting one of the light portions output from theoptical splitter section to a phase modulation using the firstsynthesized signal; a second waveguide for subjecting the other lightportion output from the optical splitter section to a phase modulationusing the second synthesized signal; and an optical synthesis sectionfor permitting optical synthesis and interference between the opticalphase modulated signal output from the first waveguide and the opticalphase modulated signal output from the second waveguide to generate theoptical packet.

A typical address reading section includes: a phase/intensity conversionsection for outputting an optical signal which is obtained by convertingoptical phase variation in one of the optical packets output from theoptical splitter section into optical intensity variation; and aphotoelectric conversion section for converting the optical signaloutput from the phase/intensity conversion section into an addresssignal. Alternatively, the address reading section may include: aphase/intensity conversion section for outputting an optical signalwhich is obtained by converting optical phase variation in one of theoptical packets output from the optical splitter section into opticalintensity variation; and a photoelectric conversion section forconverting the optical signal output from the phase/intensity conversionsection into positive and negative address signals, the negative addresssignal being obtained by inverting the polarity of the positive addresssignal, and outputting the positive address signal to the path switchingsection and the negative address signal to the optical phase adjustmentsection. Alternatively, the address reading section may include: aphase/intensity conversion section for outputting positive and negativeoptical signals, the positive optical signal being obtained byconverting optical phase variation in one of the optical packets outputfrom the optical splitter section into optical intensity variation, andthe negative optical signal being obtained by inverting the polarity ofthe positive optical signal; a first photoelectric conversion sectionfor converting the positive optical signal output from thephase/intensity conversion section into an address signal and outputtingthe address signal to the path switching section; and a secondphotoelectric conversion section for converting the negative opticalsignal output from the phase/intensity conversion section into anaddress signal, and outputting the address signal to the optical phaseadjustment section.

The photoelectric conversion section may convert an intensity of theoptical signal output from the phase/intensity conversion section tologic value 1 if the intensity is equal to or less than a predeterminedthreshold value and to logic value 0 if the intensity is greater thanthe predetermined threshold value, thereby extracting the addresssignal. In this case, the threshold value is preferably equal to orgreater than a value which is ¼ as large as a difference between anoptical intensity of the optical packet input to the optical splittersection at logic value 1 and an optical intensity of the optical packetat logic value 0, and is equal to or less than a value which is ½ aslarge as the optical intensity of the optical packet at logic value 0.

The phase/intensity conversion section may comprise a Mach-Zehnderinterferometer. The phase/intensity conversion section may output twooptical signals whose modulated components are out of phase. In the casewhere the phase/intensity conversion section outputs two optical signalswhose modulated components are out of phase, the photoelectricconversion section may comprise two photodiodes for respectivelydetecting the two optical signals output from the phase/intensityconversion section. Furthermore, the optical modulation section mayperform a phase modulation using the information signal and an intensitymodulation using the address signal.

Thus, according to the present invention, decrease in throughput due tomultiplexing of an address signal is prevented, and the transmissionpath for an optical packet can be switched based on a simple structureeven if the modulation speed for the information signal becomes high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the structure of an opticalpacket exchanger according to a first embodiment of the presentinvention.

FIG. 2 is an exemplary block diagram illustrating the details of aportion of a router section 300.

FIG. 3 is a diagram showing exemplary variations in the intensity ofelectrical signals, and exemplary variations in the phase and intensityof optical signals, which are input to or output from an optical packetexchanger.

FIG. 4 is a diagram illustrating showing exemplary input/outputcharacteristics of a first waveguide 106.

FIG. 5 is a diagram illustrating exemplary input/output characteristicsof a second waveguide 107.

FIG. 6 is another exemplary block diagram illustrating the details of aportion of a router section 300.

FIG. 7 is a block diagram illustrating the structure of an opticalpacket exchanger according to a second embodiment of the presentinvention.

FIG. 8 is a block diagram illustrating the structure of an opticalpacket exchanger according to a third embodiment of the presentinvention.

FIG. 9 is a block diagram illustrating the structure of an opticalpacket exchanger according to a fourth embodiment of the presentinvention.

FIG. 10 is a block diagram illustrating the structure of an opticalpacket exchanger according to a fifth embodiment of the presentinvention.

FIG. 11 is a block diagram illustrating the structure of a conventionaloptical packet exchanger.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 is a block diagram illustrating the structure of an opticalpacket exchanger according to a first embodiment of the presentinvention. In FIG. 1, the optical packet exchanger according to thefirst embodiment is composed of an optical transmitter section 100, anoptical transmission section 200, and a router section 300. The opticaltransmitter section 100 comprises a light source 101 and an opticalmodulation section 102. The optical modulation section 102 includes anoptical splitter section 103, a first splitter section 104, a firstsynthesis section 105, a first waveguide 106, a second waveguide 107, asecond synthesis section 108, a second splitter section 109, a phaseinversion section 110, and an optical synthesis section 111. The routersection 300 comprises an optical splitter section 301, an addressreading section 302, and a path switching section 303. The addressreading section 302 includes a phase/intensity conversion section 304and a photoelectric conversion section 305.

Hereinafter, with reference to FIG. 1, an operation of the opticalpacket exchanger having the above structure will be described.

In the optical transmitter section 100, the light source 101 outputscontinuous light. The optical splitter section 103 splits the continuouslight which is output from the light source 101, and outputs twoportions of light. The second splitter section 109 receives aninformation signal to be transmitted, and splits the information signalinto two output information signals. The first splitter section 104receives an address signal corresponding to a destination to which theinformation signal is to be transmitted, and splits the address signalinto two output address signals. The phase inversion section 110receives one of the output information signals from the second splittersection 109, inverts the phase of the information signal, and outputsthe resultant signal. The first synthesis section 105 combines one ofthe output address signals from the first splitter section 104 with theinformation signal whose phase has been inverted by the phase inversionsection 110, thereby generating a first synthesized signal D1. Thesecond synthesis section 108 combines the other output address signalfrom the first splitter section 104 with the other output informationsignal from the second splitter section 109, thereby generating a secondsynthesized signal D2.

The first waveguide 106 subjects one of the output light portions fromthe optical splitter section 103 to a phase modulation based on thefirst synthesized signal D1 which has been generated by the firstsynthesis section 105, thereby generating an optical phase modulatedsignal E1. The second waveguide 107 subjects the other output lightportion from the optical splitter section 103 to a phase modulationbased on the second synthesized signal D2 which has been generated bythe second synthesis section 108, thereby generating an optical phasemodulated signal E2. The optical synthesis section 111 permits opticalsynthesis and interference between the optical phase modulated signal E1which is output from the first waveguide 106 and the optical phasemodulated signal E2 which is output from the second waveguide 107,thereby generating an optical packet. This optical packet is transmittedto the router section 300 via the optical transmission section 200.

In the router section 300, the optical splitter section 301 splits anoptical packet which has been transmitted via the optical transmissionsection 200 into two output optical packets. The phase/intensityconversion section 304 converts optical phase variation in one of theoutput optical packets from the optical splitter section 301 intooptical intensity variation, and outputs the resultant optical signal.The photoelectric conversion section 305 converts the output opticalsignal from the phase/intensity conversion section 304 into an addresssignal. The path switching section 303 has at least one input port forreceiving the other output optical packet from the optical splittersection 301, and a plurality of output ports (FIG. 1 shows an examplewhere there are three output ports). Based on the address signal whichis output from the photoelectric conversion section 305, the pathswitching section 303 selects one of the output ports to be used foroutputting the optical packet which is output from the optical splittersection 301.

Next, the details of the phase/intensity conversion section 304 will bedescribed. FIG. 2 is an exemplary block diagram illustrating the detailsof a portion of the router section 300 shown in FIG. 1. In FIG. 2, thephase/intensity conversion section 304 is composed of, for example, aMach-Zehnder interferometer 310. The Mach-Zehnder interferometer 310includes a 1-bit delay section 311, thus having a function of splittingthe optical signal into two optical signals, a function of delaying oneof the split optical signals, and a function of combining the twooptical signals. The photoelectric conversion section 305 includes aphotodiode 312.

As described above, one of the optical packets which have been split bythe optical splitter section 301 is further split into two opticalpackets within the Mach-Zehnder interferometer 310 in thephase/intensity conversion section 304. Each of the two split opticalsignals is an optical signal which retains the same phase variation asthat of the original optical signal, but which has ½ the intensity ofthe original optical signal. One of the two split optical signals isdelayed in the 1-bit delay section 311 by a time T2, which correspondsto one bit of the address signal. Thereafter, the non-delayed opticalsignal and the delayed optical signal are combined within theMach-Zehnder interferometer 310.

In the optical packet exchanger according to the first embodiment, twooptical signals to be combined are subjected to an intensity modulationand a phase modulation. Therefore, depending on the phase which each ofthe optical signals to be combined has, the two optical signals willinterfere differently with each other at the time of synthesis.Specifically, if one of the optical signals has a phase 0, and the otheroptical signal has a phase π, the optical waves cancel each other at thetime of synthesis, so that the synthesized optical signal has a reducedintensity. On the other hand, if the two optical signals each have thesame phase of 0 or π, the optical waves enhance each other at the timeof synthesis, so that the synthesized optical signal has an increasedintensity.

FIG. 3 is a diagram showing exemplary variations in the intensity ofelectrical signals, and exemplary variations in the phase and intensityof optical signals, which are input to or output from the optical packetexchanger, shown as waveforms (a), (b), (c), (d), (e), (f), (g), (h),(i), and (j). Referring to FIG. 3, a specific example of the operationof the optical packet exchanger shown in FIG. 1 will be described. InFIG. 3, the horizontal axis represents time, and the vertical axisrepresents the intensity (amplitude or voltage) or phase of a signal.The time T1 represents a period of time corresponding to one bit of aninformation signal, and the time T2 represents a period of timecorresponding to one bit of an address signal. The exemplary signalwaveforms shown in FIG. 3 are based on the following five conditions:

1. the optical transmission section 200 has no loss;

2. the optical splitter section 301 has a split ratio of 1:1;

3. the information signal has a bit rate which is twice as large as thebit rate of the address signal;

4. the information signal consists of repetitions of “10011100”(waveform (a)); and

5. the address signal consists of repetitions of NRZ code “11010010”.

To the second splitter section 109, an information signal “10011100” isinput with an amplitude 2 a (waveform (c)). An information signal whosephase has been inverted by the phase inversion section 110 is shown aswaveform (d). To the first splitter section 104, an address signal whichhas been converted from the NRZ code “11010010” to an NRZ-I code“10011100” is input with an amplitude 2 b (waveform (b)).

One of the two split address signals (amplitude b) from the firstsplitter section 104 and one of the two split information signals(amplitude a) from the second splitter section 109 are combined by thesecond synthesis section 108 (waveform (b)+waveform (c)), whereby thesecond synthesized signal D2 having the waveform (f) is generated. Sincethe optical splitter section 103 has a split ratio of 1:1 (see condition2 above), an electrical signal whose intensity varies between the threelevels of “a+b”, “b”, and “a” is applied to the second waveguide 107.Similarly, one of the two split address signals from the first splittersection 104 and the information signal whose phase has been inverted bythe phase inversion section 110 are combined by the first synthesissection 105 (waveform (b)+waveform (d)), whereby the first synthesizedsignal D1 having the waveform (e) is generated.

FIG. 4 is a diagram illustrating exemplary input/output characteristicsof the first waveguide 106. FIG. 5 is a diagram illustrating exemplaryinput/output characteristics of the second waveguide 107. It is ensuredthat a half-wavelength voltage of the first waveguide 106 and the secondwaveguide 107 is equal to a voltage b of the address signal which isoutput from the first splitter section 104. It is also ensured thatoutput light phase when an input voltage to the first waveguide 106 iszero and an output light phase when an input voltage to the secondwaveguide 107 is voltage a are identical. The phase of the output lightfrom the first waveguide 106 and the phase of the output light fromsecond waveguide 107 vary as shown by waveform (g) and waveform (h),respectively.

The output light intensity from the optical synthesis section 111depends on a phase difference between the two light inputs.Specifically, the output light intensity is greater when there is nophase difference than when there is a phase difference. Since the twolight inputs are arranged so that there is no phase difference when theinformation signal is “1”, and there is a phase difference when theinformation signal is “0”, it is possible to vary the optical intensityin accordance with the variation in the information signal. On the otherhand, the output light from the optical synthesis section 111 has noother than the light phase which is given by the first waveguide 106 andthe second waveguide 107. The optical synthesis section 111 permitsoptical synthesis and interference between the optical signal which isoutput from the first waveguide 106 and an optical signal which isoutput from the second waveguide 107, thus sending an optical packet(waveform (i)) whose phase varies between two phases of 0 and π andwhose intensity varies between two levels which are defined as 4A and4B.

Since the optical transmission section 200 has no loss (see condition 1above) and the first optical splitter section 301 has a split ratio of1:1 (see condition 2 above), the first optical splitter section 301outputs optical signals each of which has ½ the intensity and amplitudeof those of waveform (i). In other words, each split optical signal fromthe first optical splitter section 301 has an intensity which variesbetween 2A and 2B. Since one of the split optical signals is furthersplit into two optical signals in the Mach-Zehnder interferometer 310,an optical signal is obtained which has ¼ the intensity and amplitude ofthose of waveform (i). In other words, the immediate input opticalsignal to the 1-bit delay section 311 has an intensity which variesbetween A and B.

The 1-bit delay section 311 delays one of the two split optical signalsby the time T2 corresponding to one bit of the address signal, afterwhich both split optical signals are combined within the Mach-Zehnderinterferometer 310. As a result, the phase/intensity conversion section304 outputs an optical signal whose intensity varies between the fivelevels of “2A”, “A+B”, “2B”, “A−B”, and “0” (waveform (j)). Concerningthe intensity of the optical signal, the photoelectric conversionsection 305 has a threshold value which is greater than “B−A” andsmaller than “2A”. If the output optical signal from the phase/intensityconversion section 304 has an intensity which is greater than thethreshold value, the photoelectric conversion section 305 outputs “0”;otherwise, the photoelectric conversion section 305 outputs “1”. As aresult, the address signal which has been transmitted from the opticaltransmitter section 100 can be properly determined as “11010010” in thephotoelectric conversion section 305.

Thus, in accordance with the optical packet exchanger of the firstembodiment, the optical transmitter section 100 subjects continuouslight which is output from the light source to a phase modulation usingan address signal and an intensity modulation using an informationsignal. The router section 300 splits the received optical packet intotwo optical packets, converts one of the optical packets into theaddress signal through a phase/intensity conversion and a photoelectricconversion, and determines an output port for the other optical packetbased on the address signal. Thus, decrease in throughput due tomultiplexing of an address signal is prevented, and the transmissionpath for an optical packet can be switched based on a simple structureeven if the modulation speed for the information signal becomes high.

The first embodiment illustrates a configuration where the opticaltransmitter section 100 subjects the continuous light which is outputfrom the light source to a phase modulation using an address signal andan intensity modulation using an information signal. Alternatively,another configuration may be adopted in which the optical transmittersection 100 subjects the continuous light which is output from the lightsource to an intensity modulation using an address signal, and a phasemodulation using an information signal. In this case, the addressreading section reads the address signal based on changes in the opticalintensity (intensify information). In accordance with such a variant ofthe optical packet exchanger, too, decrease in throughput due tomultiplexing of an address signal is prevented, and the transmissionpath for an optical packet can be switched based on a simple structureeven if the modulation speed for the information signal becomes high.

In the router section 300 illustrated in the first embodiment, thephase/intensity conversion section 304 outputs one optical signal, andthe photoelectric conversion section 305 detects the optical signalwhich is output from the phase/intensity conversion section 304 by usinga single photodiode (see FIG. 2). Alternatively, another configurationmay be adopted in which the phase/intensity conversion section 304outputs two optical signals whose modulated components are out of phase.Specifically, as shown in FIG. 6, the photoelectric conversion section305 may contain two photodiodes 312, and detect the two optical signalswhich are output from the phase/intensity conversion section 304 usingthe two photodiodes 312. Thus, on the basis of the two optical signals,the address signal can be detected in the photoelectric conversionsection 305 with a high accuracy and high efficiency.

Second Embodiment

FIG. 7 is a block diagram illustrating the structure of an opticalpacket exchanger according to a second embodiment of the presentinvention. In FIG. 7, the optical packet exchanger according to thesecond embodiment is composed of an optical transmitter section 120, anoptical transmission section 200, and a router section 300. The opticaltransmitter section 120 comprises a light signal source 121 and anoptical modulation section 122. The light signal source 121 includes alight source 101, a first splitter section 104, a first synthesissection 105, and a first waveguide 106. The optical modulation section122 includes a second waveguide 107, a second synthesis section 108, asecond splitter section 109, and a phase inversion section 110. Therouter section 300 has the same structure as that of the router section300 in the first embodiment.

As seen from FIG. 7, in the optical packet exchanger according to thesecond embodiment, a phase modulation function using an address signaland an intensity modulation function using an information signal, whichare performed in parallel fashion in the optical modulation section 102according to the first embodiment, are separated so that the phasemodulation and the intensity modulation are consecutively performed inthis order. Based on this structure, it becomes possible to omit anoptical splitter section and an optical synthesis section from theoptical modulation section, in addition to attaining the above-describedeffects.

Third Embodiment

FIG. 8 is a block diagram illustrating the structure of an opticalpacket exchanger according to a third embodiment of the presentinvention. In FIG. 8, the optical packet exchanger according to thethird embodiment includes an optical transmitter section 130, an opticaltransmission section 200, and a router section 300. The opticaltransmitter section 130 comprises a light signal source 131 and anoptical modulation section 132. The light signal source 131 includes alight source 101, a second waveguide 107, a second synthesis section108, a second splitter section 109, and a phase inversion section 110.The optical modulation section 132 includes a first splitter section104, a first synthesis section 105, and a first waveguide 106. Therouter section 300 has the same structure as that of the router section300 in the first embodiment.

As seen from FIG. 8, in the optical packet exchanger according to thethird embodiment, a phase modulation function using an address signaland an intensity modulation function using an information signal, whichare performed in parallel fashion in the optical modulation section 102according to the first embodiment, are separated so that the intensitymodulation and the phase modulation are consecutively performed in thisorder. Based on this structure, it becomes possible to omit an opticalsplitter section and an optical synthesis section from the opticalmodulation section, in addition to attaining the above-describedeffects.

Fourth Embodiment

FIG. 9 is a block diagram illustrating the structure of an opticalpacket exchanger according to a fourth embodiment of the presentinvention. In FIG. 9, the optical packet exchanger according to thefourth embodiment is composed of an optical transmitter section 100, anoptical transmission section 200, and a router section 340. The opticaltransmitter section 100 has the same structure as that of the opticaltransmitter section 100 in the first embodiment. The router section 340comprises an optical splitter section 301, an address reading section342, an optical phase adjustment section 347, and a path switchingsection 303. The address reading section 342 includes a phase/intensityconversion section 304 and a photoelectric conversion section 345. InFIG. 9, those component elements which also appear in FIG. 1 are denotedby the same reference numerals as those used therein, and thedescriptions thereof are omitted.

In the router section 340, the photoelectric conversion section 345performs a conversion for an output optical signal from thephase/intensity conversion section 304 to generate a “positive” (i.e.,non-inverted) address signal and a “negative” (i.e., inverted) addresssignal which is obtained by inverting the polarity of the positiveaddress signal. The optical phase adjustment section 347 receives theother one of the two split optical packets from the optical splittersection 301 and the negative address signal from the photoelectricconversion section 345, and subjects the optical packet to a phasemodulation using negative address signal. Through this process, thephase of the optical packet is adjusted to the initial phase value. Thepath switching section 303 receives the optical packet having theinitialized phase from the optical phase adjustment section 347 and thepositive address signal from the photoelectric conversion section 345.Then, based on the positive address signal, the path switching section303 determines an output port for the optical packet from among theplurality of output ports.

Thus, in the optical packet exchanger according to the fourthembodiment, the phase of the optical packet is initialized by performinganother phase modulation using the negative address signal. Thus, thephase can be maintained despite the cascade-connected router section;decrease in throughput due to multiplexing of an address signal isprevented; and the transmission path for an optical packet can beswitched based on a simple structure even if the modulation speed forthe information signal becomes high. It will be appreciated that therouter section 34 0 according to the fourth embodiment may be used inconjunction with the optical transmitter section 120 according to thesecond embodiment or the optical transmitter section 130 according tothe third embodiment.

Fifth Embodiment

FIG. 10 is a block diagram illustrating the structure of an opticalpacket exchanger according to a fifth embodiment of the presentinvention. In FIG. 10, the optical packet exchanger according to thefifth embodiment is composed of an optical transmitter section 100, anoptical transmission section 200, and a router section 350. The opticaltransmitter section 100 has the same structure as that of the opticaltransmitter section 100 in the first embodiment. The router section 350comprises an optical splitter section 301, an address reading section352, a second photoelectric conversion section 356, an optical phaseadjustment section 357, and a path switching section 303. The addressreading section 352 includes a phase/intensity conversion section 354and a first photoelectric conversion section 305. In FIG. 10, thosecomponent elements which also appear in FIG. 1 are denoted by the samereference numerals as those used therein, and the descriptions thereofare omitted.

In the router section 350, the phase/intensity conversion section 354may be composed of, for example, a Mach-Zehnder interferometer havingtwo output ports. As such, the phase/intensity conversion section 354converts optical phase variation in an optical packet which is outputfrom the optical splitter section 301 into optical intensity variation,and, from the respective output ports, outputs a positive optical signaland a negative optical signal which is obtained by inverting thepolarity of the positive optical signal. The second photoelectricconversion section 356 performs a conversion for the negative opticalsignal which is output from the phase/intensity conversion section 354to generate a negative address signal. The optical phase adjustmentsection 357 receives the other optical packet from the optical splittersection 301 and the negative address signal from the secondphotoelectric conversion section 356, and subjects the optical packet toa phase modulation using the negative address signal. Through thisprocess, the phase of the optical packet is adjusted to the initialphase value. The first photoelectric conversion section 305 performs aconversion for the positive optical signal which is output from thephase/intensity conversion section 354 to generate a positive addresssignal. The path switching section 303 receives the optical packethaving the initialized phase from the optical phase adjustment section357 and the positive address signal from the first photoelectricconversion section 305. Then, based on the positive address signal, thepath switching section 303 determines an output port for the opticalpacket from among the plurality of output ports.

Thus, in the optical packet exchanger according to the fifth embodiment,the phase of the optical packet is initialized by performing anotherphase modulation using the negative address signal. Thus, the phase canbe maintained despite the cascade-connected router section, decrease inthroughput due to multiplexing of an address signal is prevented, andthe transmission path for an optical packet can be switched based on asimple structure even if the modulation speed for the information signalbecomes high. It will be appreciated that the router section 350according to the fifth embodiment may be used in conjunction with theoptical transmitter section 120 according to the second embodiment orthe optical transmitter section 130 according to the third embodiment.

The first to fifth embodiment illustrate examples where an opticalsignal which is output from a light source is subjected to a phasemodulation using an address signal and an intensity modulation using aninformation signal. Conversely, the optical signal may be subjected toan intensity modulation using an address signal and a phase modulationusing an information signal.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an optical packet exchanger orthe like which switches the transmission path for an optical packetsignal using an address signal, in particular to the case where decreasein throughput due to multiplexing of an address signal needs to beprevented even if the modulation speed for the information signalbecomes high, for example.

1. An optical packet exchanger for switching a transmission path for anoptical packet which constitutes a burst-type optical signal,comprising: an optical transmitter section for transmitting an opticalpacket, on which an information signal and an address signalcorresponding to a transmission destination for the information signalare superposed by different modulation methods; an optical transmissionsection for propagating an optical packet transmitted from the opticaltransmitter section; and a router section for receiving the opticalpacket via the optical transmission section, and switching atransmission path for the optical packet based on the address signalwhich is extracted from the optical packet.
 2. The optical packetexchanger according to claim 1, wherein, the optical transmitter sectionincludes: a light source for outputting continuous light; and an opticalmodulation section for outputting an optical packet which is obtained bysubjecting the output light from the light source to an intensitymodulation using the information signal and a phase modulation using theaddress signal, the router section includes: an optical splitter sectionfor splitting the optical packet received via the optical transmissionsection into two optical packets; an address reading section for readingthe address signal based on phase information of one of the opticalpackets output from the optical splitter section; and a path switchingsection having a plurality of output ports and selecting, based on theaddress signal read by the address reading section, one of the pluralityof output ports from which to output the other optical packet outputfrom the optical splitter section.
 3. The optical packet exchangeraccording to claim 1, wherein, the optical transmitter section includes:a light signal source for outputting continuous light having beensubjected to an intensity modulation using the information signal; andan optical modulation section for outputting an optical packet which isobtained by subjecting the output light from the light signal source toa phase modulation using the address signal, and the router sectionincludes: an optical splitter section for splitting the optical packetreceived via the optical transmission section into two optical packets;an address reading section for reading the address signal based on phaseinformation of one of the optical packets output from the opticalsplitter section; and a path switching section having a plurality ofoutput ports and selecting, based on the address signal read by theaddress reading section, one of the plurality of output ports from whichto output the other optical packet output from the optical splittersection.
 4. (canceled)
 5. The optical packet exchanger according toclaim 1, wherein, the optical transmitter section includes: a lightsource for outputting continuous light; and an optical modulationsection for outputting an optical packet which is obtained by subjectingthe output light from the light source to an intensity modulation usingthe information signal and a phase modulation using the address signal,and the router section includes: an optical splitter section forsplitting the optical packet received via the optical transmissionsection into two optical packets; an address reading section for readingthe address signal based on phase information of one of the opticalpackets output from the optical splitter section; an optical phaseadjustment section for adjusting a phase of the other optical packetoutput from the optical splitter section to a constant phase value,based on the address signal read by the address reading section; and apath switching section having a plurality of output ports and selecting,based on the address signal read by the address reading section, one ofthe plurality of output ports from which to output the other opticalpacket whose phase has been adjusted to the constant phase value by theoptical phase adjustment section. 6-7. (canceled)
 8. The optical packetexchanger according to claim 2, wherein, the optical modulation sectioncomprises: an optical splitter section for splitting the output lightfrom the light source into two light portions; a first splitter sectionfor splitting the address signal into two address signals; a secondsplitter section for splitting the information signal into twoinformation signals; a phase inversion section for inverting a phase ofone of the information signals output from the second splitter section;a first synthesis section for combining one of the address signalsoutput from the first splitter section with the information signal whosephase has been inverted by the phase inversion section, to output afirst synthesized signal; a second synthesis section for combining theother address signal output from the first splitter section with theother information signal output from the second splitter section, tooutput a second synthesized signal; a first waveguide for subjecting oneof the light portions output from the optical splitter section to aphase modulation using the first synthesized signal; a second waveguidefor subjecting the other light portion output from the optical splittersection to a phase modulation using the second synthesized signal; andan optical synthesis section for permitting optical synthesis andinterference between the optical phase modulated signal output from thefirst waveguide and the optical phase modulated signal output from thesecond waveguide to generate the optical packet.
 9. (canceled)
 10. Theoptical packet exchanger according to claim 1, wherein, a modulationspeed for the address signal and a modulation speed for the informationsignal are different.
 11. The optical packet exchanger according toclaim 2, wherein, the address reading section includes: aphase/intensity conversion section for outputting an optical signalwhich is obtained by converting optical phase variation in one of theoptical packets output from the optical splitter section into opticalintensity variation; and a photoelectric conversion section forconverting the optical signal output from the phase/intensity conversionsection into an address signal. 12-13. (canceled)
 14. The optical packetexchanger according to claim 5, wherein, the address reading sectionincludes: a phase/intensity conversion section for outputting an opticalsignal which is obtained by converting optical phase variation in one ofthe optical packets output from the optical splitter section intooptical intensity variation; and a photoelectric conversion section forconverting the optical signal output from the phase/intensity conversionsection into positive and negative address signals, the negative addresssignal being obtained by inverting the polarity of the positive addresssignal, and outputting the positive address signal to the path switchingsection and the negative address signal to the optical phase adjustmentsection. 15-19. (canceled)
 20. The optical packet exchanger according toclaim 11, wherein, the photoelectric conversion section converts anintensity of the optical signal output from the phase/intensityconversion section to logic value 1 if the intensity is equal to or lessthan a predetermined threshold value and to logic value 0 if theintensity is greater than the predetermined threshold value, therebyextracting the address signal. 21-22. (canceled)
 23. The optical packetexchanger according to claim 20, wherein, the threshold value is equalto or greater than a value which is ¼ as large as a difference betweenan optical intensity of the optical packet input to the optical splittersection at logic value 1 and an optical intensity of the optical packetat logic value 0, and is equal to or less than a value which is ½ aslarge as the optical intensity of the optical packet at logic value 0.24-28. (canceled)
 29. The optical packet exchanger according to claim11, wherein, the phase/intensity conversion section outputs two opticalsignals whose modulated components are out of phase.
 30. (canceled) 31.The optical packet exchanger according to claim 1, wherein, the opticaltransmitter section includes: a light source for outputting continuouslight; and an optical modulation section for outputting an opticalpacket which is obtained by subjecting the output light from the lightsource to a phase modulation using the information signal and anintensity modulation using the address signal, and the router sectionincludes: an optical splitter section for splitting the optical packetreceived via the optical transmission section into two optical packets;an address reading section for reading the address signal from intensityinformation of one of the optical packets output from the opticalsplitter section; and a path switching section having a plurality ofoutput ports and selecting, based on the address signal read by theaddress reading section, one of the plurality of output ports from whichto output the other optical packet output from the optical splittersection.
 32. The optical packet exchanger according to claim 1, wherein,the optical transmitter section includes: a light source for outputtingcontinuous light; and an optical modulation section for outputting anoptical packet which is obtained by subjecting the output light from thelight source to a phase modulation using the information signal and anintensity modulation using the address signal, and the router sectionincludes: an optical splitter section for splitting the optical packetreceived via the optical transmission section into two optical packets;an address reading section for reading the address signal from intensityinformation of one of the optical packets output from the opticalsplitter section; an optical intensity adjustment section for adjustingan intensity of the other optical packet output from the opticalsplitter section to a constant intensity value, based on the addresssignal read by the address reading section; and a path switching sectionhaving a plurality of output ports and selecting, based on the addresssignal read by the address reading section, one of the plurality ofoutput ports from which to output the other optical packet whoseintensity has been adjusted to the constant intensity value by theoptical intensity adjustment section.
 33. A router for switching atransmission path for an optical packet which constitutes a burst-typeoptical signal and on which an information signal and an address signalcorresponding to a transmission destination for the information signalare superposed by different modulation methods, the router comprising:an optical splitter section for splitting the optical packet into twooptical packets; an address reading section for reading the addresssignal based on phase information of one of the optical packets outputfrom the optical splitter section; and a path switching section having aplurality of output ports and selecting, based on the address signalread by the address reading section, one of the plurality of outputports from which to output the other optical packet output from theoptical splitter section.
 34. The router according to claim 33, furthercomprising an optical phase adjustment section for adjusting a phase ofthe other optical packet output from the optical splitter section to aconstant phase value based on the address signal read by the addressreading section, and thereafter outputting the other optical packet tothe path switching section.
 35. The router according to claim 33,wherein, the address reading section includes: a phase/intensityconversion section for outputting an optical signal which is obtained byconverting optical phase variation in one of the optical packets outputfrom the optical splitter section into optical intensity variation; anda photoelectric conversion section for converting the optical signaloutput from the phase/intensity conversion section into an addresssignal.
 36. The router according to claim 34, wherein, the addressreading section includes: a phase/intensity conversion section foroutputting an optical signal which is obtained by converting opticalphase variation in one of the optical packets output from the opticalsplitter section into optical intensity variation; and a photoelectricconversion section for converting the optical signal output from thephase/intensity conversion section into positive and negative addresssignals, the negative address signal being obtained by inverting thepolarity of the positive address signal, and outputting the positiveaddress signal to the path switching section and the negative addresssignal to the optical phase adjustment section.
 37. (canceled)
 38. Therouter according to claim 35, wherein, the photoelectric conversionsection converts an intensity of the optical signal output from thephase/intensity conversion section to logic value 1 if the intensity isequal to or less than a predetermined threshold value and to logic value0 if the intensity is greater than the predetermined threshold value,thereby extracting the address signal. 39-40. (canceled)
 41. The routeraccording to claim 38, wherein, the threshold value is equal to orgreater than a value which is ¼ as large as a difference between anoptical intensity of the optical packet input to the optical splittersection at logic value 1 and an optical intensity of the optical packetat logic value 0, and is equal to or less than a value which is ½ aslarge as the optical intensity of the optical packet at logic value 0.42-46. (canceled)
 47. The router according to claim 35, wherein, thephase/intensity conversion section outputs two optical signals whosemodulated components are out of phase.
 48. (canceled)